<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box1{
            color: #0f0;
            padding: 0;
            margin-left: 0.5em;/* .5em */
            
        }
        .common{
            width: 300px;
            height: 300px;
            font:italic bold 20px '微软雅黑';
            border:1px solid red;
            margin: 10px 10px 20px 20px;/* 上右下左 */
            padding: 20;
        }
        .box2{
            color:#f00;
            padding: 10px;
        }
        .big{
            display: flex;
        }
    </style>
</head>
<body>
    <div class="big">
        <div class="common box1">简化css</div>
        <div class="common box2">简化css</div>
    </div>
</body>
</html>